In the field of humidity sensors which the present invention can be applied to, humidity sensors are classified into, according to the operation principles, a resistance sensor using a conductivity varied by moisture in porous ceramics or electrolytes, and a capacitive sensor using a permittivity (dielectric constant) variation generated when moisture is absorbed in a high-molecular polymer.
The resistance type humidity sensor is facilitated to be miniaturized and can be used in the wide range of humidity, and its response rate is fast. The capacitance type humidity sensor is made using the principle that capacitance varies with an amount of water absorbed in polymer material. The capacitance type humidity sensor has a wide humidity measuring range of 1 to 100% and it has a linear output so application circuits can be simply implemented. And also, in the area of measurement and adjustment, the capacitance type humidity sensor can work not only at room temperature but also at a temperature of −40° C. to 100° C. without a separate temperature-compensating apparatus. Further, the capacitance type humidity sensor can be easily applied to a microcomputer-utilizing circuit since it can operate on the direct current.
However, the conventional capacitance type humidity sensors, which are limited only for the microelement manufacturing field, are very expensive. Accordingly, they are not suitable for uses in agriculture, fisheries, forestry, medical treatment, hygiene and industrial fields.
In addition, in case of the field of detecting sensors for diapers, which the humidity sensor of the present invention can be used for, conventional detecting sensors for diapers generally include thin electrode films (aluminum films), that are conductive material, adhered in a given interval on a silicon or synthetic resin sheet to make a band shape. In this configuration, urine serves as a conductor which connects the electrode films electrically, and thus a urine detecting signal is detected.
The techniques for detecting urine or feces in a diaper and transmitting an alarm for the time to replace diapers have been widely proposed. However, the conventional techniques have many restrictions in materially manufacturing and putting to practical use due to a high manufacturing cost and malfunction. And the conventional techniques can be used for detecting urine by electric currents made by ions, etc., but have difficulties in detecting feces. Also, the conventional techniques have the important problem of possibly causing a sudden stimulus to a human body, since they use flow of electric currents. In other words, a voltage high enough to affect a human body can be applied between the electrodes, and urine can cause a high and abrupt electric current to flow between the electrodes, giving a sudden stimulus to a human body.